Currently, since most of processes able to form nanoscale patterns on a substrate are based on vacuum technologies, these processes are complicated and expensive. For example, electron (E)-beam lithography may form micropatterns in vacuum. However, since a region on which a pattern may be formed is relatively localized, a relatively large amount of time and costs may be necessary in order to form a micropattern over a large area. Also, with respect to photolithography used in a semiconductor process, a size of a pattern is affected by a wavelength of a light source. Thus, an expensive piece of equipment using a deep ultraviolet (UV) light source, such as a 248 nm KrF excimer laser or 193 nm ArF excimer laser, must be included in order to realize a nanoscale pattern. Nevertheless, resolution may be limited to about 0.1 μm. Therefore, new technical approaches may be required for reducing the size of the pattern as well as costs.
Mirkin and his colleagues at Northwestern University used metal nanowires in preparing electrodes having a nanospacing (see L. Qin, S. Park, L. Huang, C. A. Mirkin, Science, 309, 113-115 (2005)). Nanowires in the form of gold-silver-gold (or gold-nickel-gold) were prepared and randomly scattered on a substrate, and gold/titanium or silica (SiO2) was then deposited thereon. The gold-silver-gold (or gold-nickel-gold) nanowires were detached from the substrate through sonication and only silver (or nickel) was then selectively etched from the gold-silver-gold (or gold-nickel-gold) nanowires to form a nanospacing at a position in which silver (or nickel) existed between gold layers. Since a nanospacing having a minimum size of 5 nm may be formed in a nanowire electrode prepared through the above method, a nanoscale device having high resolution may be fabricated.
However, the foregoing process may have the following limitations; (1) Since nanowires are randomly scattered in the above process, positions and directions of nanospacings may not be accurately controlled. Since the positions and directions of the nanospacings must be controlled in order to regularly arrange nanoscale devices, the above process may not be used for integrating the nanoscale devices. (2) In order to fabricate a device by using a metal nanowire prepared by the above process, probing electrodes must be accurately deposited on both ends of the metal nanowire. Since a high cost E-beam lithography technique must be used for this purpose, the above process may not be suitable for large area or mass production. (3) The above process has poor reproducibility and thus, may be difficult to be used for a real device.
Coli at Nokia Research Center, and Ferrari and his colleagues at University of Cambridge scattered inorganic nanowires on a silicon substrate and used them as an etching mask (see A. Colli, A. Fasoli, S. Pisana, Y. Fu, P. Beecher, W. I. Miline, A. C. Ferrari, Nano Letters, 8, 1358-1362. (2008)). However, since nanowires are also randomly scattered on a substrate in this process, this process may have three limitations described above.
Therefore, there is a need to develop a method of forming a micropattern, which overcomes limitations in alignment, reproducibility, and large area or mass production described above.